Avengers Endgame may be the biggest box office hit of all time, but fans have noticed a key error in the climactic "Avengers Assemble" battle scene against evil villain Thanos (Josh Brolin).

The sequence is already iconic as we see essentially all the heroes of the Marvel Cinematic Universe gather to put an end to the monstrous titan who decimated half of the universe's population in Avengers: Infinity War.